The overall goals of the research proposed in this application are two in number. The first is the development of methods based on structural studies and in vitro tissue culture production of erythropoietin, which can lead to the acquisition of hormone for therapeutic use. Secondly, we hope to develop assay methods which can be of use in enhancing clinical studies and the investigation of erythroid kinetics. The specific aims of the present grant will be continued and expanded as follows: (1) development of a radioimmunoassay for erythropoietin to complement this laboratorie's hemagglutination inhibition assay; (2) determination of the chemical structure of erythropoietin and factors necessary for its formation; (3) utilization of immunochemical methods to identify erythropoietin's cellular sites of production and action; tissue culture techniques will be used to produce erythropoietin in bone marrow cultures; and these tissue culture techniques will be used to produce quantities of hormone for structural studies and possible therapeutic use; and (4) assessment of the role of erythropoietin in pregnancy, as well as the anemia of chronic renal disease and the anemia in cyclic-neutropenic dogs.